Significance of Patient-Reported Outcomes for Metastatic Breast Cancer Patients.

BACKGROUND: Breast cancer is still the most common malignancy in women worldwide. Once metastasized, breast cancer treatment primarily aims at reducing symptom burden, thereby trying to maintain and improve a patient's quality of life (QoL), delaying disease progression, and prolonging survival. Curing the disease is not possible in the palliative setting. To better understand metastatic breast cancer patients, their symptoms, and wishes, which are important for treatment decision making and outcome, patient-reported outcomes (PROs) are of great importance, giving an impression of what really matters to and concerns a patient. SUMMARY: Many advances have been made to implicate PROs in clinical trials, non-interventional studies, registries, and clinical routine care of metastatic breast cancer. For example, large phase III trials like PALOMA-3 (NCT01942135), MONALEESA-7 (NCT02278120), HER2CLIMB (NCT02614794), and KEYNOTE-119 (NCT02555657) trials implemented PROs in their trial design to assess the QoL of their trial patients. Also, non-interventional studies on metastatic breast cancer, e.g., the NABUCCO study (IOM-02240), and prospective non-interventional, multicenter registries, e.g., the tumor registry breast cancer (NCT01351584) or the breast cancer registry platform OPAL (NCT03417115), have implemented PROs to assess QoL during the anticancer treatment periods of the patients. KEY MESSAGE: Using PROs in metastatic breast cancer can support shared treatment decision making and management of symptoms, eventually leading to an improvement in QoL. Progressively, regulatory authorities take PROs into consideration for the approval of new drugs. Hence, the implication of PROs in cancer treatment, and especially in MBC, is of significant value.

The secreted inhibitor of invasive cell growth CREG1 is negatively regulated by cathepsin proteases.

Previous clinical and experimental evidence strongly supports a breast cancer-promoting function of the lysosomal protease cathepsin B. However, the cathepsin B-dependent molecular pathways are not completely understood. Here, we studied the cathepsin-mediated secretome changes in the context of the MMTV-PyMT breast cancer mouse model. Employing the cell-conditioned media from tumor-macrophage co-cultures, as well as tumor interstitial fluid obtained by a novel strategy from PyMT mice with differential cathepsin B expression, we identified an important proteolytic and lysosomal signature, highlighting the importance of this organelle and these enzymes in the tumor micro-environment. The Cellular Repressor of E1A Stimulated Genes 1 (CREG1), a secreted endolysosomal glycoprotein, displayed reduced abundance upon over-expression of cathepsin B as well as increased abundance upon cathepsin B deletion or inhibition. Moreover, it was cleaved by cathepsin B in vitro. CREG1 reportedly could act as tumor suppressor. We show that treatment of PyMT tumor cells with recombinant CREG1 reduced proliferation, migration, and invasion; whereas, the opposite was observed with reduced CREG1 expression. This was further validated in vivo by orthotopic transplantation. Our study highlights CREG1 as a key player in tumor-stroma interaction and suggests that cathepsin B sustains malignant cell behavior by reducing the levels of the growth suppressor CREG1 in the tumor microenvironment.

Impact of cathepsin B on the interstitial fluid proteome of murine breast cancers.

Carcinomas establish a molecular cross talk between malignant tumor cells and the activated non-malignant cells of the tumor stroma. This cell-cell communication in tumor-stroma interaction includes soluble, secreted proteins that act in a paracrine or autocrine manner. Proteases are crucial factors in tumor-stroma interaction by degrading or truncating secreted bioactive proteins. The cysteine protease cathepsin B is frequently overexpressed in several cancer types, including breast cancer. Its abundance often correlates with poor prognosis. In the murine polyoma virus middle T oncogene (PyMT) breast cancer model, cathepsin B is equally pro-tumorigenic. In this study, we investigate how cathepsin B shapes the secreted proteome of PyMT breast cancers. We employed a novel strategy to harvest tumor interstitial fluid (IF) in combination with chemical stable isotope tagging for quantitative proteomic comparison of IF stemming from PyMT tumors from wild-type mice, mice lacking cathepsin B, and mice over-expressing human cathepsin B. In three biological replicates, we achieve good proteome coverage (∼1700 proteins), with a large content (>70%) of secreted proteins. This characterizes IF as a robust source for the investigation of cancer secretomes. We also identified a large number of shed ectodomains, thus highlighting the importance of tumor-contextual cell surface proteolysis. Furthermore, IF contained >190 proteases and protease inhibitors, which span the entire range of absolute protein abundances; an observation testifying for an important role of proteolysis in tumor-stroma interaction. The cathepsin B genotype consistently affected proteins including alpha-1B-glycoprotein and major urinary proteins 11 and 8 (MUP8). Our study establishes tumor IF as a rich source for the investigation of secreted proteins in tumor biology and sheds light on complex proteolytic networks in the breast cancer secretome.